Resin-Coated Metal Pigment, Method for Producing the Same, and Water Base Paint Using the Same

ABSTRACT

The present invention provides a resin-coated metal pigment capable of achieving both of water resistance of a water base paint and chemical resistance of a film at a high level, and a water base paint using the resin-coated metal pigment. The present invention provides a method for producing a resin-coated metal pigment including an adsorption step of bringing a solution or a dispersion liquid of a phosphate ester component (A) into contact with a metal pigment to prepare a phosphate ester adsorbing metal pigment, a slurry preparation step of preparing a slurry for polymerization obtained by dissolving a polymerization component (B) therein, and a coating step of polymerizing the polymerization component (B) to form a resin coating layer on the surface of the phosphate ester adsorbing metal pigment; a resin-coated metal pigment obtained by the method; and a water base paint using the resin-coated metal pigment.

TECHNICAL FIELD

The present invention relates to a resin-coated metal pigment containedin a metallic paint or the like for use in painting of a metal or aplastic. More specifically, the present invention relates to aresin-coated metal pigment having excellent paint storage stability, inparticular, water resistance when being used as a water base paint, andexhibiting excellent chemical resistance when being formed into a film.

BACKGROUND ART

From heightened concern for an environmental problem, a water base paintor a powder paint has recently attracted the attention as lowpollution-type paints without using an organic solvent. Even in the caseof these paints, metallic decorative property is required in a diverserange of applications as in a conventional organic solvent-based paint,and therefore use of a metal pigment is indispensable. In powdercoating, an article to be coated is substantially limited to thosecontaining metal, due to restrictions of electrostatic coating andhigh-temperature baking. On the other hand, when a metal pigment is usedfor a water base paint, the metal pigment may react with water in thepaint and turn into black or generate a hydrogen gas in some cases, thuscausing a problem of poor storage stability of the paint.

The technologies for improving the storage stability of the paintinclude the followings. Japanese Patent Laying-Open No. 2-120368 (PatentDocument 1) proposes that a mixture of an organophosphate ester havingan ester residue containing a saturated aliphatic group and containingno unsaturated aliphatic group, and an organophosphate ester having anester residue containing an unsaturated aliphatic group is used as apigment component. Japanese Patent Laying-Open No. 6-57171 (PatentDocument 2) proposes that the surface of an aluminum flake is coatedwith a film of molybdic acid. International Publication WO02/031061Pamphlet (Patent Document 3) proposes an aluminum pigment capable offorming a film derived from peroxymolybdic acid, and also contains atleast one amine selected from among an alkylamine, an arylamine, analkanolamine and an alkoxylamine.

However, the metal pigment obtained by these technologies is excellentin storage stability as a water base paint, but is inferior in chemicalresistance when formed into a film. Accordingly, the use is practicallylimited only to the case where overcoat is applied, and thus there is aproblem such as low versatility.

On the other hand, in plastic coating of a cellular phone and a personalcomputer, since the article has to be ready for actual use after coatingjust once from the viewpoint of cost, excellent chemical resistance isalso required for the film in these applications. In order to solve theproblem, Japanese Patent Laying-Open No. 62-081460 (Patent Document 4)proposes a metal powder coated with a copolymer of trimethylolpropanetriacrylate and/or trimethylolpropane trimethacrylate and a small amountof acrylic acid and/or methacrylic acid. Japanese Patent Publication No.01-049746 (Patent Document 5) proposes a resin-coated metal pigment,wherein the surface of the metal pigment is coated by strong adhesionwith a highly three-dimensionalized resin made from a radicalpolymerizable unsaturated carboxylic acid and/or a phosphate mono- ordi-ester having a radical polymerizable double bond and a monomer having3 or more radical polymerizable double bonds, and the alkali resistanceis 1.0 or less and the pigment is not substantially agglomerated in aheat resistance stability test. Japanese Patent Laying-Open No.64-040566 (Patent Document 6) proposes an aluminum flake havingmicroscopically smooth surface, which is uniformly coated with acopolymer obtained by reacting at least two compounds selected from thegroup consisting of oligomers and monomers having at least onepolymerizable double bond. Japanese Patent Laying-Open No. 2005-146111(Patent Document 7) proposes a resin-coated aluminum pigment wherein thesurface of a material aluminum pigment is coated with a copolymerobtained by polymerizing a monomer having a polymerizable double bond, amonomer having a polymerizable double bond and a benzene ring, and(meth)acrylic acid.

Although these technologies satisfy the market needs in the applicationto an organic solvent-based paint, there remains a problem that waterresistance is not sufficient in the application to a water base paint.Commonly, the chemical resistance may not be improved by a surfacetreatment for imparting water resistance, while the water resistance maynot be improved by a surface treatment for imparting chemicalresistance. As a result, it is difficult to achieve both of waterresistance and chemical resistance at a sufficiently practicable level.

As a surface treatment technology combining water resistance andchemical resistance, International Publication WO96/038506 Pamphlet(Patent Document 8) proposes a resin-coated metal pigment, wherein (A)at least one kind selected from among a radical polymerizableunsaturated carboxylic acid, and/or a phosphate or phosphonate mono- ordi-ester having a radical polymerizable double bond, and/or a couplingagent having a radical polymerizable double bond, (B) a monomer having 3or more radical polymerizable double bonds and (C) a polymerizationinitiator are used, which is produced by adding the component (A) firstto treat the metal pigment, and then gradually adding at least one ofthe components (B) and (C) to form a polymerized resin layer on thesurface. Japanese Patent Laying-Open No. 2000-044835 (Patent Document 9)proposes a resin-coated metal pigment that is prepared by dispersing ametal pigment obtained by a physical vapor deposition film crushingmethod in an organic solvent, adding (A) at least one kind selected froma radical polymerizable unsaturated carboxylic acid, a phosphate orphosphonate mono- or di-ester having a radical polymerizable double bondand a coupling agent having a radical polymerizable double bond, andfurther adding (B) a monomer having 3 or more radical polymerizabledouble bonds and (C) a polymerization initiator, in which at least oneof the components (B) and (C) is gradually added, followed bypolymerization.

However, in the above patent documents, the water resistance isevaluated by an amount of gas generated as measured at 50° C. for 24hours using a paint having a pH adjusted to 9.5. Under these conditions,alkali resistance is substantially evaluated, and therefore waterresistance is not properly evaluated. In recent years, the pH of a waterbase paint is commonly adjusted within a range from about 7.5 to 8.8,and water resistance is commonly evaluated by the generation of gasduring at least several days.

In other words, the needs for a low-pollution water base metallic paintwith high versatility is increasing more and more, but the technologycapable of achieving both of water resistance and chemical resistance ata sufficiently practicable level has never been completed.

Patent Document 1: Japanese Patent Laying-Open No. 2-120368 PatentDocument 2: Japanese Patent Laying-Open No. 6-57171 Patent Document 3:International Publication WO02/031061 Pamphlet Patent Document 4:Japanese Patent Laying-Open No. 62-081460 Patent Document 5: JapanesePatent Publication No. 01-049746 Patent Document 6: Japanese PatentLaying-Open No. 64-040566 Patent Document 7: Japanese Patent Laying-OpenNo. 2005-146111 Patent Document 8: International Publication WO96/038506Pamphlet Patent Document 9: Japanese Patent Laying-Open No. 2000-044835DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to solve the above problems and toprovide a resin-coated metal pigment capable of improving paintstability, particularly water resistance of a water base paint, andsecuring chemical resistance of a film formed by applying the water basepaint at a sufficiently practicable level, and a highly versatilelow-pollution water base paint using the resin-coated metal pigment.

Means for Solving the Problems

The present invention relates to a method for producing a resin-coatedmetal pigment including an adsorption step of bringing a solution of aphosphate ester component (A) containing phosphate mono- and/or diestershaving a radical polymerizable double bond, or a dispersion liquidcontaining the phosphate ester component (A) dispersed in a solvent intocontact with a metal pigment to prepare a phosphate ester adsorbingmetal pigment containing a phosphate ester adsorbed on the surface ofthe metal pigment, a slurry preparation step of preparing a slurry forpolymerization obtained by dispersing the phosphate ester adsorbingmetal pigment in a solvent for polymerization and dissolving apolymerization component (B) including a monomer and/or an oligomerhaving at least one polymerizable double bond in the solvent forpolymerization, and a coating step of polymerizing the polymerizationcomponent (B) to form a resin coating layer on the surface of thephosphate ester adsorbing metal pigment, wherein the dispersion liquidis obtained by mixing a solution obtained by dissolving the phosphateester component (A) in a first solvent, with a second solvent, and thesolvent for polymerization is a solvent having solubility at 25° C. ofthe phosphate ester component (A) of 10 g or less with respect to 100 gof the solvent.

The present invention also relates to a method for producing aresin-coated metal pigment, wherein the slurry preparation step includesthe steps of preparing a pigment slurry in which the phosphate esteradsorbing metal pigment is dispersed in the solvent for polymerization,and mixing the polymerization component (B) with the pigment slurry.

The present invention also relates to a method for producing aresin-coated metal pigment, further including, after the absorptionstep, a step of polymerizing the phosphate ester adsorbed to thephosphate ester adsorbing metal pigment.

The present invention also relates to a method for producing aresin-coated metal pigment, wherein a polar solvent is used as thesolvent in the solution of the phosphate ester component (A).

The present invention also relates to a method for producing aresin-coated metal pigment, wherein the same kind of a solvent is usedas the second solvent and the solvent for polymerization.

The present invention also relates to a method for producing aresin-coated metal pigment, wherein the phosphate ester component (A) is2-methacryloyloxyethyl acid phosphate.

The present invention also relates to a method for producing aresin-coated metal pigment, wherein a phosphorus content per unitsurface area of the resin-coated metal pigment is within a range from0.05 to 1.3 mg/m².

The present invention also relates to a method for producing aresin-coated metal pigment, wherein the polymerization component (B)includes a monomer having at least two polymerizable double bonds.

The present invention also relates to a resin-coated metal pigmentincluding a metal pigment, a phosphate ester layer, and a resin coatinglayer that coats the metal pigment with the phosphate ester layerinterposed therebetween, wherein the phosphate ester layer is made ofphosphate mono- and/or di-esters having a radical polymerizable doublebond, or a homopolymer or a copolymer of phosphate mono- and/ordi-esters, the resin coating layer is made of a homopolymer or acopolymer obtained by polymerizing a monomer and/or an oligomer havingat least one polymerizable double bond, and a phosphorus content perunit surface area of the resin-coated metal pigment is within a rangefrom 0.05 to 1.3 mg/m².

The present invention also relates to a resin-coated metal pigment,wherein the phosphate ester layer is made of 2-methacryloyloxyethyl acidphosphate.

The present invention also relates to a water base paint including theresin-coated metal pigment and a binder.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to provide aresin-coated metal pigment capable of achieving storage stability,particularly water resistance when being used as a water base paint andchemical resistance of a film at a sufficiently practicable level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an apparatus used for measurement ofan amount of hydrogen gas generated.

FIG. 2 is a graph showing a relation between Log(elapsed time) (second)and the amount of the gas generated, measured using the apparatus shownin FIG. 1.

DESCRIPTION OF THE REFERENCE SIGNS

11: Reactor, 12: Screw cap, 13: Two-way cock, 14: Dry bath with stirrer,15, 18: Teflon (registered trademark) tube, 17: Water bath, 19:Measuring cylinder

BEST MODES FOR CARRYING OUT THE INVENTION

A method for producing a resin-coated metal pigment of the presentinvention is characterized by uniformly adsorbing a phosphate esterhaving a radial polymerizable double bond on the surface of a metalpigment to form a resin coating layer, and includes an adsorption stepof bringing a solution of a phosphate ester component (A) containingphosphate mono- and/or diesters having a radical polymerizable doublebond, or a dispersion liquid containing the phosphate ester component(A) dispersed in a solvent into contact with a metal pigment to preparea phosphate ester adsorbing metal pigment containing a phosphate esteradsorbed on the surface of the metal pigment, a slurry preparation stepof preparing a slurry for polymerization, obtained by dispersing thephosphate ester adsorbing metal pigment in a solvent for polymerizationand dissolving a polymerization component (B) including a monomer and/oran oligomer having at least one polymerizable double bond in the solventfor polymerization, and a coating step of polymerizing thepolymerization component (B) to form a resin coating layer on thesurface of the phosphate ester adsorbing metal pigment.

That is, in the present invention, the phosphate ester is adsorbed onthe surface of the metal pigment and then the resin coating layer isformed. The phosphate ester used in the present invention serves as acorrosion inhibitor for the surface of the metal pigment, while theresin coating layer used in the present invention has an action forimproving the chemical resistance of the metal pigment. Accordingly, themethod of uniformly adsorbing the phosphate ester on the surface of themetal pigment and then uniformly forming the resin coating layer overthe phosphate ester adsorbing metal pigment provides a resin-coatedmetal pigment for imparting excellent water resistance when being usedas a paint and excellent chemical resistance when being formed into afilm.

The phosphate ester component (A) used in the present invention isadsorbed on the surface of the metal pigment by the adsorption action ofan OH group in the molecule to the surface of the metal pigment. On theother hand, the phosphate ester component (A) used in the presentinvention has a radical polymerizable double bond, and thepolymerization component (B) used in the present invention has at leastone polymerizable double bond. Therefore, the phosphate ester adsorbedon the surface of the metal pigment in the adsorption step forms acovalent bond with the polymerization component (B) in the followingcoating step, and thus exerting the effect of exhibiting strongadhesiveness between the metal pigment and the resin coating layer withthe phosphate ester interposed therebetween.

<Adsorption Step>

In the adsorption step in the production method of the presentinvention, a solution of the phosphate ester component (A) or adispersion liquid composed of the phosphate ester component (A)dispersed in a solvent is brought into contact with the metal pigment.The dispersion liquid is prepared by dissolving the phosphate estercomponent (A) in a first solvent and then mixing the resultant solutionwith a second solvent. The method makes it possible to finely dispersethe phosphate ester component (A) in the dispersion liquid. That is tosay, since the phosphate ester component (A) is brought into contactwith the metal pigment in a dissolving state or finely dispersed statein the present invention, the phosphate ester is adsorbed uniformly onthe surface of the metal pigment.

As the treatment method, wherein the phosphate ester is brought intocontact with the metal pigment in a dissolving state using a solventdissolving the phosphate ester component (A), thereby uniformlyadsorbing the phosphate ester, for example, the following method can beexemplified. The metal pigment is often commercially available in apaste form containing solvent(s) such as an aliphatic hydrocarbon and/oran aromatic hydrocarbon, alone or in combination of two or more kinds ofthese solvents as a mixture solvent. These solvents are commonly thosethat do not dissolve a phosphate mono- or di-ester having a radicalpolymerizable double bond (nonsolvent) or that do dissolve but have lowsolubility (poor solvent).

A method for preparing the solution of the phosphate ester component (A)in the present invention includes a method of preliminarily replacing asolvent in a metal pigment paste with a solvent that dissolves thephosphate ester component (A), followed by the addition of the phosphateester component (A) and further kneading. The phosphate ester component(A) may be added as it is, or after diluting with a solvent thatdissolves the phosphate ester component (A).

It is also possible to employ a method in which the metal pigment pasteis diluted with a solvent that dissolves the phosphate ester component(A) and the phosphate ester component (A) is added thereto, and then themixture is kneaded or stirred. However, in this case, an aliphatichydrocarbon or aromatic hydrocarbon or the mixture solvent thereof(i.e., a poor solvent for the phosphate ester component (A)) originatedfrom the metal pigment paste and a solvent that dissolves the phosphateester component (A) (i.e., a good solvent for the phosphate estercomponent (A)) end up to be mixed in the system. Therefore, it isnecessary that the amount of the good solvent to be added is controlledto have the composition that allows the phosphate ester component (A) tobe dissolved.

It is also possible to employ a method, in which the metal pigment pasteis preliminarily replaced with a good solvent for the phosphate estercomponent (A), the metal pigment paste is dispersed in the good solventto make a slurry, and the phosphate ester component (A) is added to theresultant slurry with stirring. In this method, the next polymerizationreaction may be performed directly, or the phosphate ester adsorbingmetal pigment may be isolated in a paste form by filtration and thensupplied to the next step. In the case of performing the filtrationoperation, when the amount of the phosphate ester component (A) to beadded exceeds the saturated adsorption amount of the phosphate estercomponent (A) onto a pigment particle, the excess phosphate estercomponent (A) is discharged outside the system together with thefiltrate.

It is also possible to employ a method, in which the metal pigment pasteis dispersed in a good solvent for the phosphate ester component (A) asit is to make a slurry, and the phosphate ester component (A) is addedto the resultant slurry with stirring. In this method, since a poorsolvent originated from the metal pigment paste and a good solvent endup to be mixed in the system, the amount of the good solvent needs to becontrolled so as to have a composition that allows the phosphate estercomponent (A) to be dissolved. Either is possible that the slurry isdirectly served for the next polymerization reaction, or that the slurryis filtered to isolate the phosphate ester adsorbing metal pigment in apaste form. In the case of performing the filtration operation, when theamount of the phosphate ester component (A) to be added exceeds thesaturated adsorption amount of the phosphate ester component (A) ontothe pigment particle, the excess phosphate ester component (A) isdischarged outside the system together with the filtrate.

When a dispersion liquid of the phosphate ester component (A) is used inthe present invention, the adsorption step can be carried out asfollows. The phosphate ester component (A) is dissolved in a firstsolvent, and the resultant solution is mixed with a second solvent toprepare a dispersion liquid in which the phosphate ester component (A)is finely dispersed. In this case, a good solvent for the phosphateester component (A) is used as the first solvent, while a poor solventfor the phosphate ester component (A) or a solvent that does notdissolve the phosphate ester component (A) at all is used as the secondsolvent.

It is possible to employ a method, in which the metal pigment paste ispreliminarily replaced with the second solvent, the metal pigment pasteis dispersed in the second solvent to make a slurry, and the dispersionliquid of the phosphate ester component (A) or a solution containing thephosphate ester component (A) and the first solvent is slowly added tothe resultant slurry over 10 minutes or more with stirring. According tothe method, the phosphate ester component (A) phase-separated in thesecond solvent is uniformly adsorbed on the entire surface of the metalpigment. Either is possible that the next polymerization reaction iscarried out after the adsorption step as it is, or the phosphate esteradsorbing metal pigment is isolated in a paste form by filtration andthen supplied to the next step. However, in the case of performing thefiltration operation, when the amount of the phosphate ester component(A) to be added exceeds the saturated adsorption amount of the phosphateester component (A) onto the pigment particle, the excess phosphateester component (A) is discharged outside the system together with thefiltrate.

It is also possible to employ a method in which the metal pigment pasteis dispersed as it is in the second solvent to make a slurry, adispersion liquid of the phosphate ester component (A) or a solutioncontaining the phosphate ester component (A) and the first solvent isslowly added to the resultant slurry over 10 minutes or more withstirring, and the phase-separated phosphate ester component (A) isadsorbed on the surface of the metal pigment. In this method, since apoor solvent originated from the metal pigment paste and the secondsolvent end up to be mixed in the system, the amount of the secondsolvent needs to be controlled so as to have a composition that allowsthe phosphate ester component (A) to maintain a finely dispersed state.Either is possible that the slurry is directly served for the nextpolymerization reaction, or that the slurry is filtered to isolate thephosphate ester adsorbing metal pigment in a paste form. In the stepaccompanied by the filtration operation, when the amount of thephosphate ester component (A) to be added exceeds the saturatedadsorption amount of the phosphate ester component (A) to the pigmentparticle, the excess phosphate ester component (A) is discharged outsidethe system together with the filtrate.

The paste or slurry in which the phosphate ester component (A) isadsorbed on the metal pigment in the adsorption step is used for a nextpolymerization step. The paste or slurry obtained in the adsorption stepmay be used as it is or may be subjected to solvent replacement beforeuse. For example, when the amount of the phosphate ester component (A)to be added exceeds the saturated adsorption amount of the phosphateester component (A) onto the pigment particle, if the resultant paste orslurry is preliminarily dispersed in a poor solvent for the phosphateester component (A), the excess phosphate ester component (A) isphase-separated or precipitated to be adsorbed onto the metal pigment.Thus, the excess phosphate ester component (A) is not discharged outsidethe system by filtration. Solvent replacement may be carried out forsuch a purpose or out of constraint of the next polymerization step.

The present invention may further include a step of polymerizing thephosphate ester absorbed to the phosphate ester adsorbing metal pigmentafter the adsorption step. In this case, the phosphate ester can beadsorbed more strongly to the surface of the metal pigment. When adispersion liquid of the phosphate ester component (A) is used, adispersing agent may be added to the first or second solvent, ifnecessary, for the purpose of accelerating fine dispersion of thephosphate ester component (A).

<Metal Pigment>

Examples of the metal pigment used for the present invention include,but are not limited to, flakes of metal such as aluminum, zinc, copper,bronze, nickel, titanium and stainless, and alloy flakes thereof. Amongthese metal pigments, an aluminum flake is particularly preferredbecause it is excellent in metallic luster and is inexpensive, and isalso easy to handle due to the low specific gravity.

The metal pigment used in the present invention is preferably in a flakeform for use as a pigment for a metallic paint. The average particlesize of the metal pigment is preferably from about 1 to 100 μm, ingeneral, and more preferably from 3 to 60 μm. The average thickness ofthe metal pigment is preferably from about 0.01 to 5 μm, in general, andmore preferably from 0.02 to 2 μm.

When the average particle size of the metal pigment is 1 μm or more,metallic feeling or brightness feeling is excellent, and when theaverage particle size is 100 μm or less, a flaked particle is lesslikely to stick out on the surface of the film and the smoothness orshininess on the paint surface is favorable. When the average thicknessof the metal pigment is 0.01 μm or more, there are such advantages ashigher strength and excellent workability during the production steps,and when the average thickness is 5 μm or less, there are suchadvantages as low production cost in addition to excellent smoothness orshininess on the paint surface.

The average particle size of the metal pigment is determined bycalculating a volume average out of particle size distribution datameasured by a known particle size distribution measurement method suchas laser diffraction, a micro-mesh sieve or Coulter counter method.Further, the average thickness is calculated from hiding power anddensity of the metal pigment.

On the surface of the metal pigment used in the present invention, agrinding aid added upon grinding may be adsorbed. Examples of thegrinding aid include fatty acids such as oleic acid and stearic acid,aliphatic amines, aliphatic amides, aliphatic alcohols and estercompounds. These substances have effects of suppressing unnecessaryoxidation on the surface of the metal pigment and improving luster. Theadsorption amount of the grinding aid is preferably less than 2 parts bymass based on 100 parts by mass of the metal pigment. When the amount isless than 2 parts by mass, there is an advantage that the surface lusteris less likely to degrade.

In order to provide diverse colors to the metal pigment used in thepresent invention, various colorants and color pigments can be adheredon the surface of the metal pigment.

Examples of the colorant and the coloring pigment include, but are notparticularly limited to, quinacridone, diketo-pyrrolo-pyrrole,isoindolinone, indanthrone, perylene, perinone, anthraquinone,dioxazine, benzoimidazolone, triphenylmethane quinophthalone,anthrapyrimidine, chrome yellow, pearl mica, transparent pearl mica,colored mica, interference mica, phthalocyanine, halogenatedphthalocyanine, azo pigments (azomethine metal complexes, condensed azopigments), titanium oxide, carbon black, iron oxide, copperphthalocyanine, condensed polycyclic pigments, and the like.

A method of adhering a color pigment to the metal pigment used in thepresent invention is not particularly limited, but is preferably amethod in which a color pigment is coated with a dispersing agent andthe resultant color pigment is mixed with the metal pigment in anon-polar solvent with stirring to adhere the color pigment to the metalpigment.

As the dispersing agent, aromatic carboxylic acids such as benzoic acid,vinyl benzoate, salicylic acid, anthranilic acid, m-aminobenzoic acid,p-aminobenzoic acid, 3-amino-4-methylbenzoic acid, 3,4-diaminobenzoicacid, p-aminosalicylic acid, 1-naphthoic acid, 2-naphthoic acid,naphthenic acid, 3-amino-2-naphthoic acid, cinnamic acid andaminocinnamic acid; amino compounds such as ethylenediamine,trimethylenediamine, tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane,1,10-diaminodecane, 1,12-diaminododecane, o-phenylenediamine,m-phenylenediamine, p-phenylenediamine, 1,8-diaminonaphthalene,1,2-diaminocyclohexane, stearylpropylenediamine,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane andN-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane; aluminum ortitanium chelate compounds; and the like are preferably used.

Similarly, in order to provide diverse colors to the metal pigment usedin the present invention, an interference film or the like can be formedon the surface of the metal pigment. The method is not particularlylimited. However, for example, in order to form an optical interferenceoxidation film on the surface of each particle of the metal pigment, themethod is preferably a method in which the metal pigment is heated toabout 300 to 700° C. in an atmosphere where the amount of oxygen iscontrolled to form an air oxidation film on the surface, or a method ofcoating the metal pigment in a flake form with a precursor of an oxideof a transition metal or the like, followed by thermolysis.

<Phosphate Ester Component (A)>

It is generally known that phosphoric acid or a phosphate mono- ordi-ester is adsorbed onto the surface of a metal to act as anadsorption-type metal corrosion inhibitor. The phosphate mono- and/ordi-ester having a radical polymerizable double bond used as a phosphateester component (A) in the present invention is a substance that hasboth functions of adsorption-type metal corrosion inhibitor and radicalpolymerizability. Water resistance as one of the properties that theresin-coated metal pigment prepared by the present invention has isconsidered to be attained by uniformly adsorbing the phosphate estercomponent (A) over the surface of the metal pigment to polymerize.

Specific examples of the preferable phosphate ester component (A) usedin the present invention include 2-methacryloyloxyethyl acid phosphate,di-2-methacryloyloxyethyl acid phosphate, tri-2-methacryloyloxyethylacid phosphate, 2-acryloyloxy ethyl acid phosphate, di-2-acryloyloxyethyl acid phosphate, tri-2-acryloyloxy ethyl acid phosphate,diphenyl-2-methacryloyloxyethyl acid phosphate, diphenyl-2-acryloyloxyethyl acid phosphate, dibutyl-2-methacryloyloxyethyl acid phosphate,dibutyl-2-acryloyloxy ethyl acid phosphate,dioctyl-2-methacryloyloxyethyl acid phosphate,dioctyl-2-methacryloyloxyethyl acid phosphate, dioctyl-2-acryloyloxyethyl acid phosphate, 2-methacryloyloxy propyl acid phosphate,bis(2-chloroethyl)vinyl phosphonate, diallyldibutyl phosphonosuccinate,and the like. These phosphate ester components can be used alone or incombination of two or more kinds. Examples of the more preferablephosphate ester component (A) are phosphoric monoesters such as2-methacryloyloxyethyl acid phosphate and 2-acryloyloxy ethyl acidphosphate. Particularly, 2-methacryloyloxyethyl acid phosphate ispreferably used.

The phosphate ester component (A) of the present invention may beconstituted only by phosphate mono- and/or di-esters having radicalpolymerizability, but may further contain phosphate mono- and/ordi-esters having no radical polymerizable double bond. Examples of thephosphate mono- and/or di-esters having no radical polymerizable doublebond include methyl acid phosphate, ethyl acid phosphate, butyl acidphosphate, isodecyl acid phosphate, phenylphosphonic acid, 2-ethylhexylacid phosphate, lauryl acid phosphate, stearyl acid phosphate, oleylacid phosphate, dimethyl acid phosphate, diethyl acid phosphate, dibutylacid phosphate, diisodecyl acid phosphate, di-2-ethylhexyl acidphosphate, dilauryl acid phosphate, distearyl acid phosphate, dioleylacid phosphate, and the like.

<Solvent for Solution of Phosphate Ester Component (A)>

As a solvent for preparing a solution of the phosphate ester component(A) used in the present invention, a solvent dissolving the phosphateester component (A) may be used, and a single solvent or a mixturesolvent of two or more kinds of the solvents may be used. A preferredsolvent differs depending on the composition of the phosphate estercomponent (A), and an optimum solvent may be selected in view ofcombination with the phosphate ester component (A) to be used.

Since a unit of phosphoric acid exhibits strong polarity, the solventdissolving the phosphate ester component (A) is limited to a polarsolvent, and ketones and alcohols are recommended. Among polar solvents,water and basic solvents are inadequate. In the case of using water,when an aluminum pigment or the like is used as the metal pigment, waterand aluminum are reacted to generate hydrogen gas. In the case of usinga basic solvent, since the basic solvent forms a salt together with anacidic unit of phosphoric acid, the phosphate ester component (A) may beinsolubilized or may fail to be adsorbed on the surface of the metalpigment.

As the above solvent, the solvent having a SP value within a range from9.1 to 13, more preferably from 9.2 to 10.0, are preferably used. Thesolvent having a SP value within the above range is preferred because itis particularly excellent in solubility to the phosphate ester component(A) used in the present invention. Incidentally, the SP value in thepresent invention denotes a solubility parameter.

As the above solvent, the solvent which dissolves 50 g or more of thephosphate ester component (A) in 100 g of the solvent at 25° C. ispreferably used, and the solvent capable of dissolving the phosphateester component (A) in the solvent at any given ratio is used preferablytoo. In this case, a solution containing the phosphate ester component(A) at a desired concentration can be prepared, and thereby a sufficientamount of the phosphate ester can be adsorbed on the surface of themetal pigment.

Examples of the preferred solvent include methanol, ethanol, 1-propanol,isopropyl alcohol, n-butanol; s-butanol, t-butanol, glycerin, allylalcohol, ethylene glycol, ethylene glycol monoethyl ether, ethyleneglycol monomethyl ether, ethylene glycol monomethoxymethyl ether,diethylene glycol, acetone, acetyl acetone, methyl ethyl ketone, diethylketone, cyclohexanone, diacetone alcohol, methyl isobutyl ketone,methyl-n-butyl ketone, methyl-n-propyl ketone, dimethyl sulfoxide, andthe like.

<First Solvent>

As the first solvent, a solvent capable of serving as a good solvent forthe phosphate ester component (A) is preferably used, and the samesolvent as the solvent in the solution of the phosphate ester component(A) is preferably used.

<Second Solvent>

As the preferred second solvent, a solvent capable of providing adispersion liquid, in which the phosphate ester component (A) is finelydispersed by mixing a solution containing the phosphate ester component(A) and the first solvent with the solvent, is preferably used. It ispreferred that the second solvent in effect does not dissolve thephosphate ester component (A), and more specifically, the solubility ofthe phosphate ester component (A) in 100 g of the second solvent is 10 gor less at 25° C.

A preferred SP value of the second solvent is within a range from 7.2 to9.0, and more preferably from 7.3 to 8.8, although it may differaccording to the combination with a SP value of the first solvent thatdissolves the phosphate ester component (A) or the use proportion. Whenthe SP value is within a range from 7.2 to 9.0, the compatibility withthe first solvent dissolving the phosphate ester component (A) is good,and therefore the dispersion size of the phosphate ester component (A)in the dispersion liquid becomes finer, to allow the phosphate ester tobe adsorbed on the surface of the metal pigment uniformly.

As the combination of the first solvent and the second solvent, it ispreferred that the proportion of the first solvent in the mixturesolvent accounts for 2% by mass or more at 25° C., because thedispersion particle of the phosphate ester component (A) becomes finer.When the proportion is less than 2% by mass, the size of the dispersionparticle becomes larger, and agglutination of the pigment tends tooccur. It is more preferred that the proportion is 10% by mass or more.Incidentally, the proportion can be determined as less than 100% bymass, and may be a composition with which the phosphate ester component(A) is finely dispersed in the mixture solvent.

<Amount of Phosphate Ester Component (A) Used>

Since the amount of the phosphate ester component (A) to be used isdetermined according to the proportion to the amount of the metalpigment to be used, the amount per unit mass of the metal pigment isstated here. It is preferred that the amount of the phosphate estercomponent (A) to be used is from 0.2 to 3.0 times, more preferably from1.0 to 2.0 times, the saturated adsorption amount of the phosphate esterto the metal pigment to be used. When it is 0.2 times or more, a goodeffect of improving water resistance is obtained due to contribution ofthe phosphate ester, and when it is 3.0 times or less, the phosphateester adsorbing metal pigment is less likely to be poorly dispersed andthus poor color appearance is less likely to occur by the agglutinationof the pigment. The saturated adsorption amount is considered in generalto be within a range from about 0.5 to 5% by mass to the mass of themetal pigment, although it cannot be flatly determined as it changesaccording to a kind of a metal pigment, a specific surface area, a kindof a phosphate ester component (A) to be adsorbed, an adsorptiontemperature, and the like.

The saturated adsorption amount of the phosphate ester can be simplymeasured by the following method. A solvent of a metal pigment paste isreplaced with a solvent (a) that favorably dissolves the phosphateester. An excess phosphate ester is dissolved in the solvent (a) basedon the estimated saturated adsorption amount, and the metal pigmentreplaced with the solvent (a) is dispersed thereto to make a slurry. Theslurry is stirred to adsorb the phosphate ester onto the metal pigment.The slurry is filtered, and the residue (i.e., metal pigment) is fullywashed with the solvent (a). The resultant slurry is dried to make apowdered sample, and the phosphorus content of the sample is measuredby, for example, the following method.

About 1 g of the powdered sample is placed in a plastic vessel andprecisely weighed. 15 ml of an aqueous 6N HCl solution and 2 ml of anaqueous 13N HNO₃ solution are added to the powdered sample to dissolvethe metal components of the powdered sample completely. The resultantsolution is filtered. The filtrate is poured into a 50 ml volumetricflask, and the inner wall of the apparatus and the adhering residue arewashed with pure water into the flask. The volume is adjusted to 50 ml,and the concentration of phosphorus is measured at the wavelength of 178nm using ICP (ICPS-8000 manufactured by Shimadzu Corporation), and themeasurement value is converted into the amount of phosphorus.Separately, the residue and the filter paper are placed in a glassbeaker, and about 10 ml of 6 N nitric acid and about 5 ml of 60% by massperchloric acid are added to the glass beaker. The glass beaker isheated on a sand bath at 200° C. until the solid matter dissolvescompletely and the solution turns into transparent. Since nitric acid isevaporated during heating, nitric acid is added consecutively. Whencontinuously heated, the liquid is evaporated to generate white smoke.When the white smoke is extinct, the beaker is cooled. 10 ml of anaqueous 6N HCl solution is added thereto, and the beaker is heated todissolve the content completely. The volume of the liquid is adjustedwith a 50 ml volumetric flask, the concentration of phosphorus ismeasured using ICP in the same manner as above, and the amount ofphosphorus is calculated. The amounts of phosphorus obtained from thefiltrate and the residue are summed up, and the phosphorus content iscalculated from the weighed value of the powdered sample.

In the adsorption step, it is preferred to adjust the proportion in theamount of the metal pigment to the solution or dispersion liquid of thephosphate ester component (A), the content of the phosphate estercomponent (A) in the solution or dispersion liquid and the like so as tobring 0.3 to 10 parts by mass, preferably from 1 to 6 parts by mass, andmore preferably from 2 to 5 parts by mass of the phosphate estercomponent (A) into contact with 100 parts by mass of the metal pigment.When the amount of the phosphate ester component (A) that is broughtinto contact with 100 parts by mass of the metal pigment is 0.3 parts bymass or more, a sufficient amount of the phosphate ester is adsorbed onthe surface of the metal pigment, while when it is 10 parts by mass orless, the excessive supply of the phosphate ester component (A) isprevented, so that unnecessary increase in the production cost can beavoided, and also the agglutination of the phosphate ester absorbingmetal pigment can be prevented.

In the resin-coated metal pigment of the present invention, it ispreferred that the phosphorus content is within a range from 0.05 to 1.3mg/m² per unit surface area of the resin-coated metal pigment. When thephosphorus content is 0.05 mg/m² or more, water resistance when beingused as a paint is favorably exhibited, while when it is 1.3 mg/m² orless, unnecessary increase in the production cost can be prevented, andalso the agglutination of the phosphate ester adsorbing metal pigment isprevented.

In the present invention, whether or not the phosphate ester isuniformly adsorbed on the surface of the metal pigment is confirmed by,for example, infrared spectroscopy such as microscopic infraredspectroscopy.

<Polymerization Component (B)>

It is preferred that the polymerization component (B) used in thepresent invention is a monomer and/or an oligomer having at least onepolymerizable double bond, and preferably a combination of two or morekinds selected from the monomer and/or oligomer having at least onepolymerizable double bond, from the viewpoints of prevention ofagglutination accompanying polymerization, improvement in smoothness ofa resin film (i.e., densification) and improvement of the alkaliresistance accompanying thereto. Specifically, the monomer and oligomerdisclosed in Japanese Patent Laying-Open No. 64-40566 is recommended. Inthe present invention, it is considered that excellent chemicalresistance is exhibited when a film is formed using a paint containingthe resin-coated metal pigment, because a resin film composed of thepolymerization component (B) is formed on the surface of the metalpigment.

Examples of the polymerization component (B) are preferably at least onekind of, more preferably at least two kinds of, acrylates andmethacrylates such as isoamyl acrylate, lauryl acrylate, stearylacrylate, butoxyethyl acrylate, ethoxy-diethylene glycol acrylate,methoxy-triethylene glycol acrylate, methoxy-polyethylene glycolacrylate, methoxydipropylene glycol acrylate, phenoxyethyl acrylate,phenoxy-polyethylene glycol acrylate, tetrahydrofurfuryl acrylate,isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethylsuccinic acid,2-acryloyloxyethylphthallic acid,2-acryloyloxyethyl-2-hydroxyethylphthallic acid, triethylene glycoldiacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate,1,9-nonanediol diacrylate, dimethylol-tricyclodecane diacrylate,trimethylol propane triacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate,2-hydroxy-3-acryloyloxypropyl methacrylate, isooctyl acrylate,isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycolacrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthallicacid, hydroxypivalic acid neopentyl glycol diacrylate, polytetraethyleneglycol diacrylate, ditrimethylolpropane tetraacrylate, methylmethacrylate, ethyl methacrylate, n-butyl methacrylate, isobutylmethacrylate, 2-ethylhexyl methacrylate, isodecyl methacrylate, n-laurylmethacrylate, tridecyl methacrylate, n-stearyl methacrylate,methoxydiethylene glycol methacrylate, methoxypolyethylene glycolmethacrylate, cyclohexyl methacrylate, tetrahydrofurfural methacrylate,benzyl methacrylate, phenoxyethyl methacrylate, isobornyl methacrylate,2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,2-hydroxybutyl methacrylate, 2-methacryloyloxyethylsuccinic acid,2-methacroyloxyethyl hexahydrophthallic acid,2-methacryloyloxyethyl-2-hydroxypropyl phthalate, ethylene glycoldimethacrylate, diethylene glycol dimethacrylate, 1,4-butanedioldimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanedioldimethacrylate, trimethylolpropane trimethacrylate, glycerindimethacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, t-butylmethacrylate, isostearyl methacrylate, methoxytriethylene glycolmethacrylate, n-butoxyethyl methacrylate, 3-chloro-2-hydroxypropylmethacrylate, triethylene glycol dimethacrylate, neopentyl glycoldimethacrylate, in addition, styrene, α-methylstyrene, vinyltoluene,divinylbenzene, acrylonitrile, methacrylonitrile, vinyl acetate, vinylpropionate, isoprene, chloroprene, vinylidene chloride, acrylamide,methyl vinyl ketone, phenyl vinyl ketone, methyl vinyl ether, phenylvinyl ether, N-vinyl pyrrolidone, N-vinylcarbazole, polybutadiene,epoxidated polybutadiene, cyclohexene vinyl monoxide, and divinylbenzenemonoxide. However, the component is not limited thereto. Among these,the use of a monomer and/or an oligomer having two or more polymerizabledouble bonds as the polymerization component (B) is advantageous interms of further improvement in the chemical resistance because offormation of a resin coating layer containing a resin formingthree-dimensional cross linkage.

<Slurry Preparation Step>

In the slurry preparation step, a slurry for polymerization is prepared,in which the phosphate ester adsorbing metal pigment is dispersed in asolvent for polymerization that will be described later, and also thepolymerization component (B) is dispersed in the solvent forpolymerization. A method for preparation of the slurry includes, forexample, a method in which a pigment slurry is prepared by dispersing aphosphate ester adsorbing metal pigment in a solvent for polymerization,followed by mixing the pigment slurry with the polymerization component(B).

<Coating Step>

In the present invention, after the adsorption step of uniformlyadsorbing the phosphate ester component (A) on the metal pigment, thepolymerization component (B) is added thereto, a monomer and/or anoligomer of the polymerization component (B) is polymerized using aradical initiator or the like, and a resin coating layer is formed onthe surface of the metal pigment. At this time, an adsorbing layerincluding the phosphate ester can be formed on the surface of the metalpigment by preliminarily polymerizing the phosphate ester component (A)adsorbed onto the metal pigment using a radical initiator or the like,and then the polymerization component (B) is added into the system andpolymerized with a radical initiator or the like, to form theresin-coating layer including the polymerization component (B). Further,the resin coating layer may be formed by adding the polymerizationcomponent (B) to the metal pigment to which the phosphate ester isadsorbed, and then polymerizing the phosphate ester component (A) andthe polymerization component (B) simultaneously with a radical initiatoror the like. When the phosphate ester component (A) and thepolymerization component (B) are simultaneously polymerized, a radicalpolymerizable double bond of the phosphate ester component (A) and apolymerizable double bond of the polymerization component (B) form acovalent bond between the phosphate ester component (A) and thepolymerization component (B) and thereby a copolymer is formed, so thata more uniform and stronger adsorption layer and a resin coating layerare formed on the surface of the metal pigment. Accordingly, waterresistance of the paint and chemical resistance of the film improve.Incidentally, the method disclosed in Japanese Patent Laying-Open No.64-40566 can be applied to the coating step of the present invention,but the present invention is not limited thereto.

In the coating step, a solvent for polymerization is used when thepolymerization component (B) is polymerized. As the solvent forpolymerization, a solvent that does not dissolve the phosphate esteradsorbed on the surface of the metal pigment in the adsorption step isused, and the same solvent as the second solvent above may be used.Specifically, a solvent for polymerization having the solubility at 25°C. of the phosphate ester component (A) of 10 g or less with respect to100 g thereof is used.

Examples of the preferable solvent for polymerization include aliphatichydrocarbons such as hexane, heptane, octane, cyclohexane and mineralspirit, aromatic hydrocarbons such as benzene, xylene and toluene,halogenated hydrocarbons such as chlorobenzene, trichlorobenzene,perchloroethylene and trichloroethylene, alcohols such as methanol,ethanol, 1-propanol, isopropyl alcohol, n-butanol, s-butanol andt-butanol, ketones such as acetone, acetylacetone, methyl ethyl ketone,diethyl ketone, cyclohexanone, methyl isobutyl ketone, methyl-n-butylketone and methyl-n-propyl ketone, esters such as ethyl acetate andpropyl acetate, and ethers such as tetrahydrofuran, diethyl ether andethyl propyl ether.

It is preferred that a polymerization initiator is used in the coatingstep, and particularly, a radical initiator commonly known as a radicalgenerator can be used. Specific examples of the polymerization initiatorinclude peroxides such as benzoyl peroxide, lauroyl peroxide, isobutylperoxide and methyl ethyl ketone peroxide, and azo compounds such asAIBN (azobisisobutyronitrile).

Here, it is preferred that the amount of the polymerization initiator tobe mixed is 0.1 parts by mass or more based on 100 parts by mass of thepolymerization component (B) to be fed, and more preferably 0.5 parts bymass or more. Further, it is preferred that the amount to be mixed is 10parts by mass or less, and more preferably 8 parts by mass or less. Itis preferred that the amount of the polymerization initiator to be mixedis 0.1 parts by mass or more, because the polymerization reactionproceeds certainly and an expected amount of a resin film is easilyformed. It is preferred that the amount to be mixed is 10 parts by massor less, because rapid processing of the polymerization is prevented, apolymer to be produced is adsorbed onto a metal pigment particlecertainly, and rapid increase in viscosity of the entire system andcoagulation due to the generation of a free polymer particle areprevented with the amount.

In the coating step, the polymerization reaction temperature isdetermined depending on a kind of a polymerization initiator to be used.The half life of the polymerization initiator is determined primarily bytemperature. It is preferred that the temperature is adjusted such thatthe half life of the polymerization initiator is 5 minutes or more, andmore preferably 15 minutes or more.

Also, it is preferred that the temperature is adjusted so as to make thehalf life of the polymerization initiator 20 hours or less, and morepreferably 10 hours or less. When AIBN is used as the polymerizationinitiator, for example, the half life is 22, 5, 1.2 and 0.3 hours at 60,70, 80 and 90° C., respectively, and therefore a range between 70 and90° C. is a preferred temperature range. When the polymerizationreaction is carried out at a temperature where the half life of thepolymerization initiator becomes 20 hours or less, the temperature ispreferred because a problem that the polymerization reaction hardlyproceeds is less likely to occur, and when the polymerization reactionis carried out at a temperature with which the half life of thepolymerization initiator becomes 5 minutes or more, the temperature ispreferred because rapid proceeding of the polymerization reaction isprevented, a polymer to be generated is adsorbed to a metal pigmentparticle certainly, and rapid increase in viscosity of an entire systemand coagulation due to generation of a free polymer particle areprevented.

In the coating step, it is of advantage to carry out the polymerizationreaction under an inert gas atmosphere such as nitrogen, helium or argonin order to raise the polymerization yield.

The present invention also relates to a resin-coated metal pigment thathas a metal pigment, a phosphate ester layer and a resin coating layerthat coats the metal pigment with the phosphate ester layer interposedtherebetween, wherein the phosphate ester layer is a phosphate estercontaining phosphate mono- and/or di-esters having a radicalpolymerizable double bond or a homopolymer or a copolymer of phosphatemono- and/or di-esters, the resin coating layer is a homopolymer or acopolymer prepared by polymerization of a monomer and/or an oligomerhaving at least one polymerizable double bond, and the phosphoruscontent per unit surface area of the resin-coated metal pigment fallswithin a range from 0.05 to 1.3 mg/m².

The resin-coated metal pigment provides favorable water resistance whenbeing used as a paint and favorable chemical resistance when beingformed into a film because of the phosphate ester layer formed on thesurface of the metal pigment, and the resin coating layer formed furtherthereon.

The phosphate ester layer can for example be formed by the adsorptionstep described above, and the resin coating layer can for example beformed by the coating step described above.

It is preferred that the resin coating layer contains a resin withthree-dimensional cross linkage. In such a case, better chemicalresistance is provided by the film. Incidentally, whether or not theresin coating layer contains a resin with three dimensional crosslinkage can be confirmed, for example, by a dissolution extraction testusing diverse solvent species.

<Paint>

The resin-coated metal pigment of the present invention can be used bymixing it with a known or common water base paint. An example of thepreferred water base paint includes the water base paint containing theabove described resin-coated metal pigment and a binder. These paintsare not necessarily a one part type, but may be those used by mixing twoor more parts and may be accompanied by a reaction. The water base paintcontaining the resin-coated metal pigment of the present invention cancontain other pigments and dyes to serve for the intended color phase.However, it is desired that the other pigments are used within a rangethat the metallic texture of the pigment of the present invention is notdamaged. The binder is not particularly limited as long as it is the onethat is commonly used, but an emulsion binder is preferred. As theemulsion binder, various natural or synthetic polymers, oligomers,prepolymers or the like can be used. These paints can contain variousadditives according to need. Examples of the additives include asurfactant, a stabilizer, a corrosion inhibitor, a plasticizer, apigment wetting agent, a pigment dispersing agent, a fluidity adjustingagent, a leveling agent, a fungicide, an ultraviolet absorber, and thelike.

EXAMPLES

The present invention will now be described in detail by way of examplesand comparative examples, but the present invention is not limited tothe following examples.

<Evaluation on Amount of Resin Coated>

In about 100 g of normal hexane, about 20 g of a resin-coated metalpigment paste was dispersed and the dispersion liquid was filtered. Theresidue was fully washed with normal hexane on the filter, spread over atray and dried overnight at 80° C. to give a powdered sample. About 1 gof the powdered sample was placed in a 500 ml plastic vessel andprecisely weighed (the weight was defined as a). About 100 ml of amixture acid (concentrated hydrochloric acid: concentrated nitricacid:water=1:1:2 (by volume)) was added into the above plastic vessel,and the mixture was stirred with a glass rod to dissolve the metalcomponent in the powdered sample. Then, the content of the plasticvessel was filtered using a glass fiber filter a weight of which hadbeen precisely weighed in advance (the weight was defined as b). Theresidue was fully washed with pure water on the glass fiber filter paperand then filtered. The glass fiber filter and the residue weretransferred into another plastic vessel a weight of which had beenprecisely weighed in advance (the weight was defined as c), and all theresidue adhering on the sidewall of the glass fiber filter was washed upwith pure water into the plastic vessel. The content of the plasticvessel was dried overnight in an oven at 105° C., and then preciselyweighed (the weight was defined as d). The amount of the resin to becoated (g) based on 100 g of the metal component was calculated from thefollowing equation:

(Amount of resin to be coated based on 100 g of metalcomponent)(g)=(d−b−c)/(a−(d−b−c))×100.

<Specific Surface Area>

The specific surface area of the resin-coated metal pigment or a metalpigment without resin coating was measured using an automatic specificsurface area analyzer, Macsorb HM model-1208, manufactured by MOUNTECHCo., Ltd. The powdered sample prepared above was charged in an exclusivemeasuring vessel up to about 80% and precisely weighed. The weight wasinput in the measurement instrument. The resin-coated metal pigment wasdeaerated at 250° C. for 30 minutes, or the metal pigment without resincoating was deaerated at 350° C. for 30 minutes, and measurement wascarried out under a mixture gas consisting of 30% by volume of nitrogenand 70% by volume of helium.

<Phosphorus Content>

About 1 g of the powdered sample prepared above was placed in a plasticvessel and precisely weighed. To the powdered sample, 15 ml of anaqueous 6N HCl solution and 2 ml of an aqueous 13N HNO₃ solution wereadded to completely dissolve the metal component in the powdered sample.The resultant solution was filtered. The filtrate was poured into a 50ml volumetric flask, and the inner wall of the apparatus and theadhering residue were washed with pure water. The volume was adjusted to50 ml, and the concentration of phosphorus was measured at a wavelengthof 178 nm using ICP (ICPS-8000 manufactured by Shimadzu Corporation).The measurement value was converted into the amount of phosphorus.Separately, the residue and the filter paper were placed in a glassbeaker, and about 10 ml of 6N nitric acid and about 5 ml of 60% by massperchloric acid were added to the glass beaker. The glass beaker washeated on a sand bath at 200° C. until the solid matter dissolvedcompletely and the solution turned into transparent. Since nitric acidwas gradually evaporated during heating, nitric acid was addedconsecutively. When continuously heated, the liquid was evaporated togenerate white smoke. When the white smoke was extinct, the beaker wascooled. Into the glass beaker, 10 ml of an aqueous 6N HCl solution wasadded, and the beaker was heated to dissolve the content completely. Thevolume of the liquid was adjusted with a 50 ml-volumetric flask, theconcentration of phosphorus was measured using ICP in the same manner asabove, and the amount of phosphorus was calculated. The amounts ofphosphorus obtained from the filtrate and the residue were summed up,and the phosphorus content was calculated from the weight of thepowdered sample.

<Alkali Resistance>

The resin-coated metal pigment was dispersed in an alkaline solution,being a mixture solvent, of polypropylene glycol monomethyl ether:aqueous 0.1N KOH solution=1:1 (by volume) with stirring at a constanttemperature, and the amount of hydrogen gas generated due to degradationby an alkali was diachronically measured. As the results of measurement,the value Log(elapsed time) was plotted on the horizontal axis, and theamount of the gas generated was plotted on the vertical axis. The linearpart in the range where the gas discharge velocity was stabilized wasextrapolated as zero amount of the gas generated, and the onset time ofgas discharge was defined as Log T. Since the onset time of gasdischarge depends on the particle size of the metal pigment, the onsettime of gas discharge of the material metal pigment was measured (it wasdefined as Log T′) for correction, and alkali resistance was evaluatedusing the following equation:

Log T−Log T″=Log(T/T′)=Δ Log T.

As Δ Log T increases, alkali resistance is excellent. The specificmethod will be described in the following.

The amount of the sample added to the alkaline solution above was 0.09 gas a metal component. Since the amount of the hydrogen gas that wasdiachronically generated was measured in the present measurement, it wasnecessary that the addition of the sample was carried outinstantaneously and the system was closed instantaneously immediatelyafter the addition in order to collect the gas to be generated.Therefore, the sample was dispersed in propylene glycol monomethyl etherto make a slurry, and 1 ml of the slurry was supposed to be added with amicropipette. The concentration of the slurry was adjusted so as tocontain the sample in an amount of 0.09 g as a metal component in 1 mlof the added slurry. The sample slurry was prepared as follows. About 1g of a powdered sample prepared in the same manner as above was placedin a plastic vessel and precisely weighed. The amount of the resincoated based on 100 g of the metal component of the sample waspreliminarily measured. Here, when the metal component of the sample wasaluminum and the amount of the resin coated based on 100 g of aluminumwas defined as (A) g, propylene glycol monomethyl ether was added to thesample in an amount that the dilution rate became (1050/(100+A)) timesthe weight, and the mixture was stirred to be uniformly dispersed.Aluminum contained in 1 ml of the slurry was 0.09 g.

(Method for Measuring Amount of Gas Generated)

FIG. 1 is a schematic view showing an apparatus used to measure anamount of a hydrogen gas generated. A 100 ml glass screw bottle sealedwith a screw cap 12 is used as a reactor tank 11. A Teflon (registeredtrademark) two-way cock 13 is mounted on screw cap 12, to which a tipend of a micropipette can be inserted. An entire system is kept at aconstant temperature (40° C.) by a dry bath 14 with a stirrer, and areaction solution is constantly stirred with a stirrer tip. Immediatelyafter charging a sample in, two-way cock 13 is closed to make the systema closed one. The hydrogen gas generated from the reactor tank reaches awater tank 17 by way of a Teflon (registered trademark) tube 15 andpresses up water in the water tank. The water pressed up is poured intoa measuring cylinder 19 by way of a Teflon (registered trademark) tube18, so that the amount of a hydrogen gas generated is measured bymeasuring the water volume in the measuring cylinder.

(Measurement of Amount of Gas Generated)

Using the apparatus shown in FIG. 1, the amount of the gas generated wasmeasured. In reactor tank 11, 50 ml of an aqueous 0.1N KOH solution and50 ml of propylene glycol monomethyl ether were placed with a graduatedtransfer pipette, a stirrer tip was placed, and the reactor tank was seton dry bath 14 with a stirrer. A thermoelectric couple was inserted fromtwo-way cock 13, and after confirming that the inner temperature reached40±0.5° C., 1 ml of the slurry prepared by the above-described methodwas charged in reactor tank 11 with a micropipette. As the metalpigment, 7610N manufactured by TOYO ALUMINIUM K.K. was used. Immediatelyafter completion of charging, two-way cock 13 was closed, and astopwatch was started to record the elapsed time and the amount of thegas generated.

FIG. 2 is a graph showing a relation between Log(elapsed time) (second)and the amount of the gas generated measured by the apparatus shown inFIG. 1. The elapsed time is shown by logarithm with a base of 60. Forexample, Log(elapsed time)=1 denotes 1 minute, and Log(elapsed time)=2denotes 1 hour. In the region where the gas discharge velocity isstable, the plotted points on the coordinate with Log (elapsed time) onthe horizontal axis and the amount of the gas generated on the verticalaxis almost align on a linear line, so that the point where the linearpart is extrapolated to zero amount of the gas generated (that is,intersection point with X-axis) is defined as the onset time of gasdischarge, Log T. FIG. 2 shows an example using the same sample, butchanging the amount of the sample to be added by way of changing theconcentration of the slurry to be added. Although the gas dischargevelocity depends on the amount of the sample to be added, Log T, a pointwhere the linear part is extrapolated to zero amount of the gasgenerated, does not depend on the amount of the sample to be added.Accordingly it is learned that the amount of the sample to be added doesnot exert any effect on the data as long as the aluminum component isnot far from 0.09 g. It was found that the error of Log T in the presentmeasurement was about ±0.02 as a result of confirmation of repeatedreproductivity.

The value of Log T depends on a particle size of the metal pigment. Whenthe particle size of the metal pigment is less, the specific surfacearea in general tends to be greater, the contact area with an alkaliincreases and the onset time of gas discharge becomes shorter. In orderto confirm the improvement effect of alkali resistance as a result ofresin coating, correction has to be made for the effect incurred by theparticle size of the metal pigment. Therefore, in each example andcomparative example, the onset time of gas discharge was measured forthe material aluminum pigment (it was defined as Log T′), and alkaliresistance was evaluated from the following equation:

Log T−Log T′=Log(T/T′)=Δ Log T.

That is to say, as Δ Log T increases, excellence in alkali resistanceincreases. The case where Δ Log T is 0.1 or more was rated as “Good”,while the case of less than 0.1 was rated as “Poor”.

<Water Resistance>

Using a sample paste of each example and each comparative example, awater base paint was prepared. A glass vessel was charged with 200 g ofthe water base paint. The vessel was allowed to stand in a constanttemperature water circulation tank at 40° C. and the amount of thehydrogen gas generated was measured. Water resistance was evaluated bythe amount of the gas generated 2 days after immersion in the constanttemperature water tank. The case where the amount of gas generated 2days after immersion in the constant temperature water tank was lessthan 5 ml was rated as “Good”, while the case of 5 ml or more was ratedas “Poor”.

(Preparation of Water Base Paint)

A pigment paste (X) g that is equivalent to 7.5 g of the resin-coatedmetal pigment was placed in a plastic vessel, butyl cellosolve (15−(X))g was added, and the mixture was fully stirred with a glass rod to beuniform. Then, 8.0 g of N-methyl pyrrolidone, followed by 28.0 g of purewater were added to the mixture in order, and the mixture was stirred tobe uniform in the same manner each time a compound was added. To theslurry, 140 g of an aqueous acrylic emulsion (E-208 manufactured byMitsui Chemicals, Inc.) was added, and stirred for 10 minutes by amixer-type disperser to be uniform to give a water base paint. The pH ofthe water base paint was 7.56.

<Method for Manufacturing Coated Sheet>

The water base paint prepared was spray coated on a plastic sheet. Theresultant sprayed coated sheet was dried at room temperature for about 5minutes, and baked at 60° C. for 20 minutes to give a coated sheet. Thecoated sheet was coated so as to have a coated film thickness of 10 to20 μm.

Each example and comparative example will be described hereinafter.Metal pigment pastes were all manufactured products obtained by washingwith mineral sprit. That is, the metal pigment paste was washed twicewith mineral sprit of the same kind as that contained in the paste, on afilter under suction filtration. The paste was then kneaded by a kneadermixer to be uniform, the amount of a nonvolatile component was measured,mineral spirit was added so as to set the amount of the nonvolatilecomponent to the amount of the original paste, the paste was kneadedonce again, and the nonvolatile component was adjusted and confirmed.

Example 1

In 640 g of methyl ethyl ketone (hereinafter referred to as MEK), 420 gof an aluminum paste containing an aluminum pigment as the metal pigment(7640NS manufactured by TOYO ALUMINIUM K.K., nonvolatile component of65.1% by mass, average particle size of 16 μm, specific surface area of5.5 m²/g) was dispersed and the dispersion liquid was filtered. To theresultant filter paste, 400 g of MEK was further added to replace all ofthe solvent contained in the paste with MEK. A kneader mixer was chargedwith 440.7 g of the obtained paste, and the paste was kneaded for 10minutes to be uniform. 10 g of the paste was taken out and the amount ofthe nonvolatile component was measured. The amount of the nonvolatilecomponent was 60.0% by mass. This reveals that 258.4 g of the aluminumpigment was charged in the kneader mixer.

In 46.5 g of MEK, 5.17 g of 2-methacryloyloxyethyl acid phosphate (tradename: LIGHT ESTER P-1M manufactured by Kyoeisha Chemical Co., Ltd.) wasdissolved. The resultant solution was slowly added to the above pastewhile the paste was being kneaded, and after adding the solution, themixture was further kept kneading for 5 minutes to complete theadsorption step. The amount of the nonvolatile component was measured,and it was found that the amount of the nonvolatile component containedin the paste of the phosphate ester adsorbing metal pigment on which2-methacryloyloxyethyl acid phosphate was adsorbed was 53.6% by mass.That is, the amount of the phosphate ester to be added was 2.0% by massbased on the aluminum pigment and when it was converted into per unitsurface area of the aluminum pigment, it amounted to 3.7 mg/m².

In a 1 L-separable flask, 139.9 g of the above phosphate ester adsorbingmetal pigment paste and 370.0 g of mineral spirit were placed and themixture was stirred as introducing nitrogen gas, and the temperature ofthe system was raised to 80° C. Subsequently, 7.5 g oftrimethylolpropane trimethacrylate (LIGHT ESTER TMP manufactured byKyoeisha Chemical Co., Ltd.) was added thereto to complete the slurrypreparation step. A solution of 0.75 g of azobisisobutyronitrile(reagent) dissolved in 8.5 g of MEK was added thereto, and the resultantsolution was polymerized at 80° C. for 5 hours to carry out resincoating (coating step). After the completion of the polymerization, theslurry was cooled to room temperature, filtered, fully washed withmineral spirit and kneaded to be uniform, and a paste containing aresin-coated aluminum pigment was obtained as the resin-coated metalpigment. The nonvolatile component of the paste was 48.3% by mass, andthe amount of the resin coated was 11.3 g based on 100 g of an aluminumcomponent. As a result of quantitative analysis of phosphorus, theresin-coated aluminum pigment obtained by powdering the paste contained0.29% by mass of phosphorus. According to the measurement of thespecific surface area, it was found that the specific surface area ofthe resin-coated aluminum pigment was 8.2 m²/g, and that the pigmentcontained 0.36 mg/m² of phosphorous when the measured value wasconverted into per unit surface area.

Example 2

In 640 g of MEK, 420 g of an aluminum paste containing an aluminumpigment as the metal pigment (1440YL manufactured by TOYO ALUMINIUMK.K., nonvolatile component of 71.0% by mass, average particle size of31 μm, specific surface area of 1.7 m²/g) was dispersed and thedispersion liquid was filtered. To the resultant filter paste, 400 g ofMEK was further added to replace all of the solvent contained in thepaste with MEK. A kneader mixer was charged with 455.8 g of the obtainedpaste, and the paste was kneaded for 10 minutes to be uniform. Theamount of the nonvolatile component was measured as 64.6% by mass. Thisreveals that 288.0 g of the aluminum pigment was charged in the kneadermixer.

In 16.0 g of MEK, 1.78 g of 2-methacryloyloxyethyl acid phosphate of thesame kind as in Example 1 was dissolved. The resultant solution wasslowly added to the above paste while the paste was being kneaded, andafter adding the solution, the mixture was further kept kneading for 5minutes to complete the adsorption step. The amount of the nonvolatilecomponent was measured, and it was found that the amount of thenonvolatile component contained in the paste of the phosphate esteradsorbing metal pigment on which 2-methacryloyloxyethyl acid phosphatewas adsorbed was 61.5% by mass. The amount of the phosphate ester to beadded was 0.6% by mass based on the aluminum and when it was convertedinto per unit surface area, it amounted to 3.6 mg/m².

In a 1 L-separable flask, 121.9 g of the above phosphate ester adsorbingmetal pigment paste and 370.1 g of mineral spirit were placed and themixture was stirred as introducing nitrogen gas, and the temperature ofthe system was raised to 80° C. Subsequently, 2.3 g oftrimethylolpropane trimethacrylate was added thereto to complete theslurry preparation step. A solution of 0.75 g of azobisisobutyronitrile(reagent) dissolved in 19.1 g of MEK was added thereto, and theresultant solution was polymerized at 80° C. for 5 hours to carry outresin coating (coating step). After the completion of thepolymerization, the slurry was cooled to room temperature, filtered,fully washed with mineral spirit and kneaded to be uniform, and a pastecontaining a resin-coated aluminum pigment was obtained as theresin-coated metal pigment. The nonvolatile component of the paste was77.3% by mass, and the amount of the resin coated was 3.8 g based on 100g of an aluminum component. As a result of quantitative analysis ofphosphorus, the resin-coated aluminum pigment obtained by powdering thepaste contained 0.10% by mass of phosphorus. According to themeasurement of the specific surface area, it was found that the specificsurface area of the resin-coated aluminum pigment was 2.0 m²/g, and thatthe pigment contained 0.49 mg/m² of phosphorous when the measured valuewas converted into per unit surface area.

Example 3

In 640 g of MEK, 420 g of an aluminum paste containing an aluminumpigment as the metal pigment (5680NS manufactured by TOYO ALUMINIUMK.K., nonvolatile component of 70.8% by mass, average particle size of8.7 μm, specific surface area of 10.4 m²/g) was dispersed and thedispersion liquid was filtered. To the resultant filter paste, 400 g ofMEK was further added to replace all of the solvent contained in thepaste with MEK. A kneader mixer was charged with 449.5 g of the obtainedpaste, and the paste was kneaded for 10 minutes to be uniform. Theamount of the nonvolatile component was measured as 64.1% by mass. Thisreveals that 281.7 g of the aluminum pigment was charged in the kneadermixer.

In 60.3 g of MEK, 10.7 g of 2-methacryloyloxyethyl acid phosphate of thesame kind as in Example 1 was dissolved. The resultant solution wasslowly added to the above paste while the paste was being kneaded, andafter adding the solution, the mixture was further kept kneading for 5minutes to complete the adsorption step. The amount of the nonvolatilecomponent was measured, and it was found that the amount of thenonvolatile component contained in the paste of the phosphate esteradsorbing metal pigment on which 2-methacryloyloxyethyl acid phosphatewas adsorbed was 57.0% by mass. The amount of the phosphate ester to beadded was 3.8% by mass based on the aluminum and when it was convertedinto per unit surface area, it amounted to 3.6 mg/m².

In a 1 L-separable flask, 131.5 g of the above phosphate ester adsorbingmetal pigment paste and 370.0 g of mineral spirit were placed and themixture was stirred as introducing nitrogen gas, and the temperature ofthe system was raised to 80° C. Subsequently, 14.2 g oftrimethylolpropane trimethacrylate was added thereto to complete theslurry preparation step. A solution of 0.75 g of azobisisobutyronitrile(reagent) dissolved in 13.8 g of MEK was added thereto, and theresultant solution was polymerized at 80° C. for 5 hours to carry outresin coating (coating step). After the completion of thepolymerization, the slurry was cooled to room temperature, filtered,fully washed with mineral spirit and kneaded to be uniform, and a pastecontaining a resin-coated aluminum pigment was obtained as theresin-coated metal pigment. The nonvolatile component of the paste was45.7% by mass, and the amount of the resin coated was 25.2 g based on100 g of an aluminum component. As a result of quantitative analysis ofphosphorus, the resin-coated aluminum pigment obtained by powdering thepaste contained 0.48% by mass of phosphorus. According to themeasurement of the specific surface area, it was found that the specificsurface area of the resin-coated aluminum pigment was 15.0 m²/g, andthat the pigment contained 0.32 mg/m² of phosphorous when the measuredvalue was converted into per unit surface area.

Example 4

In 640 g of MEK, 420 g of an aluminum paste of the same kind as inExample 1 was dispersed and the dispersion liquid was filtered. To theresultant filter paste, 400 g of MEK was further added to replace all ofthe solvent contained in the paste with MEK. A kneader mixer was chargedwith 454.0 g of the obtained paste, and the paste was kneaded for 10minutes to be uniform. The amount of the nonvolatile component wasmeasured as 59.5% by mass. This reveals that 264.2 g of the aluminumpigment was charged in the kneader mixer.

In 11.9 g of MEK, 1.3 g of 2-methacryloyloxyethyl acid phosphate of thesame kind as in Example 1 was dissolved. The resultant solution wasslowly added to the above paste while the paste was being kneaded, andafter adding the solution, the mixture was further kept kneading for 5minutes to complete the adsorption step. The amount of the nonvolatilecomponent was measured, and it was found that the amount of thenonvolatile component contained in the paste of the phosphate esteradsorbing metal pigment on which 2-methacryloyloxyethyl acid phosphatewas adsorbed was 56.7% by mass. The amount of the phosphate ester to beadded was 0.5% by mass based on the aluminum and when it was convertedinto per unit surface area, it amounted to 0.9 mg/m².

In a 1 L-separable flask, 132.2 g of the above phosphate ester adsorbingmetal pigment paste and 370.2 g of mineral spirit were placed and themixture was stirred as introducing nitrogen gas, and the temperature ofthe system was raised to 80° C. Subsequently, 7.5 g oftrimethylolpropane trimethacrylate was added thereto to complete theslurry preparation step. A solution of 0.75 g of azobisisobutyronitrile(reagent) dissolved in 8.7 g of MEK was added thereto, and the resultantsolution was polymerized at 80° C. for 5 hours to carry out resincoating (coating step). After the completion of the polymerization, theslurry was cooled to room temperature, filtered, fully washed withmineral spirit and kneaded to be uniform, and a paste containing aresin-coated aluminum pigment was obtained as the resin-coated metalpigment. The nonvolatile component of the paste was 55.7% by mass, andthe amount of the resin coated was 11.0 g based on 100 g of an aluminumcomponent. As a result of quantitative analysis of phosphorus, theresin-coated aluminum pigment obtained by powdering the paste contained0.06% by mass of phosphorus. According to the measurement of thespecific surface area, it was found that the specific surface area ofthe resin-coated aluminum pigment was 7.0 m²/g, and that the pigmentcontained 0.09 mg/m² of phosphorous when the measured value wasconverted into per unit surface area.

Example 5

In 640 g of cyclohexanone, 400 g of an aluminum paste of the same kindas in Example 1 was dispersed and the dispersion liquid was filtered. Tothe resultant filter paste, 400 g of cyclohexanone was further added toreplace all of the solvent contained in the paste with cyclohexanone. Akneader mixer was charged with 410.0 g of the obtained paste, and thepaste was kneaded for 10 minutes to be uniform. The amount of thenonvolatile component was measured as 54.2% by mass. This reveals that216.8 g of the aluminum pigment was charged in the kneader mixer.

In 10.9 g of cyclohexanone, 4.3 g of 2-methacryloyloxyethyl acidphosphate of the same kind as in Example 1 was dissolved. The resultantsolution was slowly added to the above paste while the paste was beingkneaded, and after adding the solution, the mixture was further keptkneading for 5 minutes to complete the adsorption step. The amount ofthe phosphate ester to be added was 2.0 g based on aluminum and when itwas converted into per unit surface area, it amounted to 3.6 mg/m².

In a 2 L stainless steel beaker, 500 g of mineral spirit was placed andintensively stirred with a propeller stirrer. The paste prepared abovewas added into the beaker and the mixture was dispersed. The resultantslurry was filtered, 200 g of mineral spirit was further added thereto,and the solvent contained in the paste was replaced with mineral spiritonce again. The nonvolatile component was measured and as a result, thenonvolatile component contained in the paste of the phosphate esteradsorbing metal pigment to which 2-methacryloyloxyethyl acid phosphatewas adsorbed was 60.5% by mass.

In a 1 L-separable flask, 123.9 g of the above phosphate ester adsorbingmetal pigment paste and 388.0 g of mineral spirit were placed and themixture was stirred as introducing nitrogen gas, and the temperature ofthe system was raised to 80° C. Then, 6.1 g of epoxidated polybutadiene(trade name: ADK CIZER-BF-1000 manufactured by ADEKA CORPORATION)diluted to 50% by mass with mineral sprit, 3.5 g of trimethylolpropanetriacrylate (trade name: TMPTA-N manufactured by DAICEL-UCB CO., LTD.),1.0 g of divinylbenzene (trade name: DVB-570 manufactured by SANKYOCHEMICAL INDUSTRIES, LTD.) and 0.75 g of azobisisobutyronitrile(reagent) were added thereto, which was polymerized at 80° C. for 6hours to carry out resin coating (coating step).

After the completion of the polymerization, the slurry was cooled toroom temperature, filtered, fully washed with mineral spirit and kneadedto be uniform, and a paste containing a resin-coated aluminum pigmentwas obtained as the resin-coated metal pigment. The nonvolatilecomponent of the paste was 52.4% by mass, and the amount of the resincoated was 10.2 g based on 100 g of an aluminum component. As a resultof quantitative analysis of phosphorus, the resin-coated aluminumpigment obtained by powdering the paste contained 0.17% by mass ofphosphorus. According to the measurement of the specific surface area,it was found that the specific surface area of the resin-coated aluminumpigment was 7.0 m²/g, and that the pigment contained 0.24 mg/m² ofphosphorous per unit surface area.

Example 6

In a 1 L-separable flask, 115.2 g of the aluminum paste of the same kindas in Example 1 and 356.0 g of mineral spirit were placed and themixture was stirred as introducing nitrogen gas, and the aluminumpigment was uniformly dispersed. In 36.5 g of MEK, 1.5 g of2-methacryloyloxyethyl acid phosphate of the same kind as in Example 1was dissolved, and the solution was slowly added dropwise to the slurrybeing stirred over 20 minutes using a dropping funnel. It was confirmedat this point that 2-methacryloyloxyethyl acid phosphate was finelydispersed in the slurry. The slurry was kept stirring for additional 40minutes to adsorb phosphate ester to the aluminum pigment. Thetemperature of the system was raised to 80° C., to which 7.5 g oftrimethylolpropane trimethacrylate, followed by a solution of 0.75 g ofazobisisobutyronitrile (reagent) dissolved in 7.6 g of MEK were added.It was polymerized at 80° C. for 5 hours to carry out resin coating.

After the completion of the polymerization, the slurry was cooled toroom temperature, filtered, fully washed with mineral spirit and kneadedto be uniform, and a paste containing a resin-coated aluminum pigmentwas obtained as the resin-coated metal pigment. The nonvolatilecomponent of the paste was 58.4% by mass, and the amount of the resincoated was 11.7 g based on 100 g of an aluminum component. As a resultof quantitative analysis of phosphorus, the resin-coated aluminumpigment obtained by powdering the paste contained 0.27% by mass ofphosphorus. According to the measurement of the specific surface area,it was found that the specific surface area of the resin-coated aluminumpigment was 7.6 m²/g, and that the pigment contained 0.35 mg/m² ofphosphorous when the measured value was converted into per unit surfacearea.

Comparative Example 1

The present comparative example was carried out by the method inaccordance with Example 1 described in Japanese Patent Publication No.01-049746. In the present comparative example, adsorption of phosphateester onto the metal pigment was not carried out, and resin coatingalone was carried out. In a 1 L-separable flask, 115.2 g of the aluminumpaste of the same kind as in Example 1 and 440.0 g of mineral spiritwere placed and the mixture was stirred as introducing nitrogen gas, andthe temperature of the system was raised to 80° C. Then, 0.38 g ofacrylic acid (manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD.) wasadded thereto to continue stirring at 80° C. for 30 minutes. The amountof acrylic acid to be added was 0.5% by mass based on aluminum, and whenit was converted into per unit surface area, it was 0.9 mg/m². Next, 7.5g of trimethylolpropane trimethacrylate and 0.75 g ofazobisisobutyronitrile (reagent) were added to carry out polymerizationat 80° C. for 5 hours.

After the completion of the polymerization, the slurry was cooled toroom temperature, filtered, fully washed with mineral spirit and kneadedto be uniform, and a paste containing a resin-coated aluminum pigmentwas obtained. The nonvolatile component of the paste was 52.6% by mass,and the amount of the resin coated was 11.5 g based on 100 g of analuminum component.

Comparative Example 2

The present comparative example was carried out by the method inaccordance with Example 3 described in International PublicationWO02/031061 Pamphlet. In the present comparative example, resin coatingto the metal pigment was not carried out, and adsorption of phosphateester alone was carried out. A kneader mixer was charged with 100 g ofthe aluminum paste of the same kind as in Example 1, and 20 g of3-(2-ethylhexyloxy)propyl amine was added thereto and the mixture waskneaded for 5 minutes. To 100 g of an aqueous solution of hydrogenperoxide containing 30% by mass of hydrogen peroxide, 8 g of powderedmetal molybdenum was added little by little, the mixture was reacted,the resultant solution was dissolved in 175 g of isopropyl alcohol, andthe solution was added to the above paste and the mixture was kneaded at60° C. for another one hour. 10 g of oleyl acid phosphate was dissolvedin 100 g of dipropylene glycol monomethyl ether to make a solution, andthe solution was added to the paste and the mixture was kneaded at roomtemperature for another 30 minutes. The nonvolatile component of thepaste was measured as 63.2% by mass.

Comparative Example 3

The present comparative example was carried out by the method inaccordance with Example 10 described in Japanese Patent Publication No.01-049746. In a 1 L-separable flask, 115.2 g of the aluminum paste ofthe same kind as in Example 1 and 399.8 g of mineral spirit were placedand the mixture was stirred as introducing nitrogen gas, and thetemperature of the system was raised to 80° C. Then, 0.39 g of2-methacryloyloxyethyl acid phosphate of the same kind as in Example 1was added thereto, and the paste was kept stirring at 80° C. for 30minutes. The amount of the phosphate ester to be added was 0.5% by massbased on aluminum and when it was converted per unit surface area, itamounted to 0.9 mg/m². Next, 7.5 g of trimethylolpropane trimethacrylate(LIGHT ESTER TMP manufactured by Kyoeisha Chemical Co., Ltd.) and 0.75 gof azobisisobutyronitrile (reagent) were added to carry outpolymerization at 80° C. for 5 hours.

After the completion of the polymerization, the slurry was cooled toroom temperature and filtered, and then observed. Since it was foundthat a particle aggregate of about 1 mm was mixed, the slurry waswet-sieved using a screen with a mesh size of 150 μm and the particleaggregate was separated. The particle aggregate was then washed withhexane, and air-dried overnight. 0.48 g of the particle aggregate wasobtained. The slurry that passed through the screen was filtered, fullywashed with mineral spirit, and kneaded to be uniform to give a pastecontaining a resin-coated aluminum pigment. The nonvolatile component ofthe paste was 50.0% by mass, and the amount of the resin coated was 11.3g based on 100 g of the aluminum component. As a result of quantitativeanalysis of phosphorus in the resin-coated aluminum pigment obtained bypowdering the paste and the particle aggregate, phosphorus was notdetected from the resin-coated aluminum pigment, and 12.82% by mass ofphosphorus was detected from the particle aggregate.

Prior to the experiment of Comparative Example 3, as a preliminary test,440 g of mineral spirit and 0.36 g of 2-methacryloyloxyethyl acidphosphate were placed in a 1 L-separable flask, and the mixture wasstirred at 80° C. for 30 minutes as introducing nitrogen gas. In thissystem, 2-methacryloyloxyethyl acid phosphate was not dissolved at allin mineral spirit and phase separated.

TABLE 1 Examples 1 2 3 4 5 6 Aluminum pigment 7640NS ^((Note 1)) 1440YL^((Note 2)) 5680NS ^((Note 3)) 7640NS 7640NS 7640NS Monomer species inadsorption MP ^((Note 4)) MP MP MP MP MP step Amount of monomer adsorbed2.0 0.6 3.8 0.5 2.0 2.0 (% by mass/Al) Amount of monomer adsorbed 3.73.6 3.6 0.9 3.7 3.7 (mg/m²) Amount of resin coated (g/100 g 11.3 3.825.2 11.0 10.2 11.7 Al) Specific surface area after resin 8.2 2.0 15.07.0 7.0 7.6 coating (m²/g) Phosphorus content (% by mass) 0.29 0.10 0.480.06 0.17 0.27 Phosphorus content (mg/m²) 0.36 0.49 0.32 0.09 0.24 0.35Alkali LogT 0.80 1.10 0.68 0.73 0.90 0.80 resistance ΔLogT 0.22 0.460.16 0.15 0.31 0.22 Water Amount of paint 0.0 2.6 0.1 0.3 0.7 3.6resistance gas generated (ml) Evaluation on alkali resistance Good GoodGood Good Good Good Evaluation on water resistance Good Good Good GoodGood Good

TABLE 2 Comparative Examples 1 2 3 Aluminum pigment 7640NS 7640NS 7640NSMonomer species in adsorption AA ^((Note 5)) — MP step Amount of monomeradsorbed (% 0.5 0.0 0.5 by mass/Al) Amount of monomer adsorbed 0.9 0.00.9 (mg/m²) Amount of resin coated (g/100 g 11.5 0.0 11.3 Al) Specificsurface area after resin — — 7.2 coating (m²/g) Phosphorus content (% bymass) 0.00 — <0.02 Phosphorus content (mg/m²) 0.00 — <0.03 Alkali LogT0.65 0.58 0.57 resistance ΔLogT 0.07 −0.01 −0.01 Water Amount of paintgas 10.0 0.0 >20 resistance generated (ml) Evaluation on alkaliresistance Poor Poor Poor Evaluation on water resistance Poor Good Poor^((Note 1)) 7640NS is manufactured by TOYO ALUMINIUM K.K. (nonvolatilecomponent of 65.1% by mass, average particle size of 16 μm, specificsurface area of 5.5 m²/g). ^((Note 2)) 1440YL is manufactured by TOYOALUMINIUM K.K. (nonvolatile component of 71.0% by mass, average particlesize of 31 μm, specific surface area of 1.7 m²/g). ^((Note 3)) 5680NS ismanufactured by TOYO ALUMINIUM K.K. (nonvolatile component of 70.8% bymass, average particle size of 8.7 μm, specific surface area of 10.4m²/g). ^((Note 4)) MP is 2-methacryloyloxyethyl acid phosphate (tradename: LIGHT ESTER P-1M) manufactured by Kyoeisha Chemical Co., Ltd.^((Note 5)) AA is acrylic acid manufactured by OSAKA ORGANIC CHEMICALINDUSTRY LTD.

As shown in Table 1 and Table 2, the results indicate that theperformance of both alkali and water resistance is not good enough inComparative Example 1 where acrylic acid was adsorbed onto the metalpigment, and then a resin coating layer was formed. The performance ofalkali resistance in Comparative Example 2 is not good enough, wheresurface treatment for the purpose of providing water resistance wascarried out, but neither adsorption of a phosphate ester nor formationof a resin coating layer were carried out. In Comparative Example 3,although a phosphate ester was brought into contact with the metalpigment before conducting a coating treatment to form a resin coatinglayer, the performance of both alkali and water resistance is not goodenough since the phosphate ester was directly added to mineral spirit, apoor solvent for a phosphate ester, and therefore the phosphate esterwas not brought into contact with the metal pigment in a dissolved stateor a finely dispersed state.

On the other hand, it can be understood that, when the resin-coatedmetal pigment of Examples 1 to 6 were used, it is possible to reconcilewater resistance of a water base paint and chemical resistance of a filmat a favorable level.

It should be construed that embodiments and examples disclosed hereinare only illustrative in all respects, and not limitative. It isintended that the scope of the present invention is indicated not by thedescription provided above but by the claims, and all meaningsequivalent to the claims and all modification within the scope of claimsare included in the present invention.

INDUSTRIAL APPLICABILITY

According to the present invention, it becomes possible to provide aresin-coated metal pigment for obtaining a water base paint havingstorage stability, particularly improved water resistance, and a filmhaving improved chemical resistance. By using the resin-coated metalpigment of the present invention in a water base paint, a film havingexcellent chemical resistance is obtained even when a single-layeredfilm is formed.

1. A method for producing a resin-coated metal pigment comprising: anadsorption step of bringing a solution of a phosphate ester component(A) containing phosphate mono- and/or diesters having a radicalpolymerizable double bond, or a dispersion liquid containing saidphosphate ester component (A) dispersed in a solvent into contact with ametal pigment to prepare a phosphate ester adsorbing metal pigmentcontaining a phosphate ester adsorbed on the surface of said metalpigment; a slurry preparation step of preparing a slurry forpolymerization obtained by dispersing said phosphate ester adsorbingmetal pigment in a solvent for polymerization and dissolving apolymerization component (B) including a monomer and/or an oligomerhaving at least one polymerizable double bond in said solvent forpolymerization; and a coating step of polymerizing said polymerizationcomponent (B) to form a resin coating layer on the surface of saidphosphate ester adsorbing metal pigment, wherein said dispersion liquidis obtained by mixing a solution obtained by dissolving said phosphateester component (A) in a first solvent, with a second solvent, and saidsolvent for polymerization is a solvent having solubility at 25° C. ofsaid phosphate ester component (A) of 10 g or less with respect to 100 gof said solvent.
 2. The method for producing a resin-coated metalpigment according to claim 1, wherein said slurry preparation stepincludes the steps of: preparing a pigment slurry in which saidphosphate ester adsorbing metal pigment is dispersed in said solvent forpolymerization; and mixing said polymerization component (B) with saidpigment slurry.
 3. The method for producing a resin-coated metal pigmentaccording to claim 1, further comprising, after said absorption step, astep of polymerizing the phosphate ester adsorbed to said phosphateester adsorbing metal pigment.
 4. The method for producing aresin-coated metal pigment according to claim 1, wherein a polar solventis used as a solvent in the solution of said phosphate ester component(A).
 5. The method for producing a resin-coated metal pigment accordingto claim 1, wherein the same kind of a solvent is used as said secondsolvent and said solvent for polymerization.
 6. The method for producinga resin-coated metal pigment according to claim 1, wherein saidphosphate ester component (A) is 2-methacryloyloxyethyl acid phosphate.7. The method for producing a resin-coated metal pigment according toclaim 1, wherein a phosphorus content per unit surface area of saidresin-coated metal pigment is within a range from 0.05 to 1.3 mg/m². 8.The method for producing a resin-coated metal pigment according to claim1, wherein said polymerization component (B) includes a monomer havingat least two polymerizable double bonds.
 9. A water base paintcomprising the resin-coated metal pigment prepared by the methodaccording to any one of claims 1 to 8, and a binder.
 10. A resin-coatedmetal pigment comprising a metal pigment, a phosphate ester layer, and aresin coating layer that coats said metal pigment with said phosphateester layer interposed therebetween, wherein said phosphate ester layeris made of a phosphate ester containing phosphate mono- and/or di-estershaving a radical polymerizable double bond, or a homopolymer or acopolymer of phosphate mono- and/or di-esters, said resin coating layeris made of a homopolymer or a copolymer obtained by polymerizing amonomer and/or an oligomer having at least one polymerizable doublebond, and a phosphorus content per unit surface area of saidresin-coated metal pigment is within a range from 0.05 to 1.3 mg/m². 11.The resin-coated metal pigment according to claim 10, wherein saidphosphate ester layer is made of a homopolymer or a copolymer obtainedfrom 2-methacryloyloxyethyl acid phosphate.
 12. A water base paintcomprising the resin-coated metal pigment according to claim 10 or 11,and a binder.